Recently, hydraulic equipment and fire-resistant hydraulic fluid applications have realized a substantial growth in usage. The Federal Coal Mine Health and Safety Act of 1969 and the Occupational Health and Safety Act (OHSA) require specific safety standards which are expected to lead to new applications and increased usage of fire-resistant functional fluids including lubricants.
Emulsions provide an important source of functional fluids having very low inflammability. Of these, the water-in-oil emulsion is the most recent and most important development. All of the emulsions and functional fluids herein discussed are of this type. In these fluids, water is the dispersed phase and oil is the continuous phase. The stability and homogeneity of the fluid is maintained by the addition of an emulsifier. The choice of the emulsifier is critical, and the emulsion is normally very sensitive to temperature variation or temperature cycling from hot to cold to hot, etc.
An emulsion deteriorates by undergoing emulsion inversion and water separation in whole or in part. Inversion is defined as the change from a water-in-oil emulsion to an oil-in-water emulsion, i.e., after inversion the mineral oil is no longer the continuous phase and water separation can be observed. As a result of such emulsion deterioration, the anti-wear property of the emulsion is decreased very substantially thereby producing premature hydraulic pump failure. The choice of emulsifier is critically important in preventing deterioration of the emulsion over a reasonable period of use and a range of temperatures, U.S. Pat. No. 3,378,494.